(1) Field of the Invention
The present invention relates to the production of gypsum wallboard, and more particularly is concerned with a method for cutting gypsum wallboard by means of a high velocity fluid cutting jet to increase the rate of production.
(2) Prior Art
The conventional process for making gypsum wallboard comprises forming an aqueous slurry of calcium sulfate hemihydrate, and depositing the slurry between two sheets of gypsum board cover sheet paper on a continuous conveyor belt having a reach length of from about 200 to about 1000 ft. The belt may be operated at a speed of 50-200 ft. per minute and typically about 110 ft. per minute. As the deposited slurry and paper travel, the calcium sulfate hemihydrate continually combines with the water in the slurry. The slurry first goes through a phase termed the initial stiffening or initial set, and subsequently reaches a Vicat set. After the Vicat set the board is conventionally cut by means of rotary knives. If the board is cut substantially before the gypsum has reached the Vicat set, the knives will not properly cut the board. Because of the softness of the gypsum material, there is a tendency for the knives either to mash the ends of the boards or for the boards to hang up because of an impression made in the board (the paper not being cleanly cut on both the top and bottom of the board). The necessity for postponing the cutting of the board until the gypsum at the cutting area has reached a Vicat set and almost a temperature rise set places a limit in the speed at which the belt may be moved and thus the rate at which the production of gypsum board takes place.